I'm trying to translate the following:
[...] quem autem valorem aliter nisi appropinquando cognoscere non datur.
Which comes from Euler (De Serie Lambertina/e). But I'm having trouble sorting out what's what. A literal translation might be
[...] which value however otherwise even if knowing to be approached is not given.
The issue I'm having is the combined use of a gerundive (or gerund), appropinquando ('to be approached, ought to be approached') with the infinite cognoscere ('to know, knowing, to be familiar with') followed by a passive verb, datur ('to be given'). All this is in a clause using both 'nisi...' ('even if, if not') and non. To make matters more confusing for me, 'quem valorem' seems like it could be used in an indirect statement with cognoscere, but then I don't know what the dative or ablative gerund and the passive verb are referring to, or how to translate it anyway.
How does this construction work, and how is the sentence translated idiomatically to English?